1. FIELD OF THE INVENTION
The present invention relates to an insulating film for semiconductor devices, and a method for making the same. More particularly, it relates to an insulating film in a multi-layer interconnection structure of two or more layers with a polymer resin film interposed between the interconnection layers, and a method for making the same.
2. DESCRIPTION OF THE PRIOR ART
It has hitherto been the practice to cover a semiconductor device with a polymer resin film and to thus improve the stability and reliability of the semiconductor device. This polymer resin, however has been disadvantageous in that it is prone to exfoliate due to an inferior adhesive property. In a semiconductor integrated circuit, especially a monolithic integrated circuit, a desired interconnection pattern has been produced in such way that a conductor metal, such as aluminum, is evaporated onto a silicon wafer in which elements such as transistors are made, and that the metal at unnecessary parts is removed by well-known photolithographic techniques or that the metal at unnecessary parts is oxidized to form an insulator by anodization employing an electrolyte.
In order to further construct one or more conductor layers on the conductor layer thus produced, a desired interconnection pattern has been formed in such a manner that a film of silicon dioxide is deposited by chemical vapor deposition, RF-sputtering or a similar well-known process, that the silicon dioxide film at parts necessary for the collection of the conductor is thereafter provided with connection or through-holes by well-known photolithography, and that the conductor metal is subsequently evaporated. This prior-art method of manufacture has had the disadvantages that the metal of the second layer is liable to be opened or disconnected on account of a step due to the interconnection conductor of the first layer or a step due to the connection-hole in the insulating film at the connection part between the conductor layers, and that pinholes tend to appear in the insulating film in, for example, a portion in which the first and second layers of the interconnection conductor cross each other, to easily short-circuit the two conductor layers which oppose each other with the insulating film held therebetween. With the process in which, after the evaporation of aluminum, the area other than the interconnection parts is anodized into aluminum oxide, steps at the crossing parts of the interconnection conductor layers are hardly generated. The steps at the connection parts between the layers, however, are still present, so that the second layer interconnection is liable to be disconnected at these parts. Moreover, the aluminum oxide film formed by the anodic oxidation is disadvantageous in being porous and having a poor insulating property.
In order to eliminate the disadvantages of the prior-art method discussed above, there has been proposed a resin insulation method which employs a heat-resistive polymer resin. By applying a prepolymer solution and heating and curing it, the steps can be compensated to form an insulating film having a flat surface. This is advantageous in that the second layer conductor undergoes substantially no disconnection at the stepped portions. The heat-resisting polymer material, however, has the disadvantage of the poor adhesive property, and requires care in its use for the insulating film.